The present invention relates to a wind turbine and, in particular, to a gearbox interposed between a rotor of a wind turbine and an electrical generator.
It is known to use a planetary gearbox to drive an electric generator in response to rotation of a rotor of a wind turbine. The rotor provides a low speed, high torque input to the gearbox. The gearbox provides a high speed, low torque output to the generator. This type of gearbox has been used in this application for approximately twenty years. Generally, planetary gear assemblies include a plurality of planet gears operatively connected at one end to a planet carrier. The planet gears engage and move within a ring gear that is a stationary or floating circular gear having inner diameter gear teeth. In addition, the planet gears are positioned in mating relationship with a sun gear, which rotates responsive to the rotation of the planet gears. Torque produced by the wind turbine rotor is transmitted into the gearbox through the planet carrier. Each stage of the three-stage gearbox increases the input speed and reduces the torque until the output speed matches the capability of a generator operatively connected to the gearbox.
During operation of the wind turbine, the gear configuration of the planet, ring and sun gears produces an axial thrust on the ring gear in an upwind direction or toward the rotor or input end of the gearbox. Under certain transient events, such as a mechanical or electrical failure that causes the wind turbine to suddenly shut down, the ring gear may experience an axial thrust or movement toward the output end of the gearbox. Gearboxes are typically adapted to restrain such axial movement and maintain alignment of the gears.
In some gearboxes the ring gear is simply affixed to the interior of the gearbox housing to restrain axial movement of the ring gear. In gearboxes that incorporate a “floating” ring gear design, the ring gear is not affixed directly to gearbox housing. With respect to FIG. 8, there is illustrated gearbox having a gearbox housing with an input housing 126 mounted to a middle housing 127. A planet gear 128 is supported on a planet carrier (not shown) and engaging the ring gear 129. The ring gear 129 includes a plurality of splines 130 disposed on the outside diameter of the ring gear 129, which splines 130 are positioned in mating relationship with internal splines 131 formed in the input housing 126. The internal splines 131 form a first lip 132 on the housing 126 that overlaps at least a portion of each spline 130 to restrain axial movement of the ring gear toward the input end of the gearbox 125. A second lip 133 that is formed at the junction of the input housing 126 and the middle housing 127 restrains movement of the ring 128 in the opposite direction.
The components of the above-described gearbox are installed in a determined order. For example, the planet carrier is first installed in the input housing 126 then the ring gear 128 is mounted in the input housing 126 by mating the splines 130 on the ring gear 128 with the corresponding internal splines 131 formed on the interior of the input housing 126. The middle housing 127 is then mounted to the input housing 126. As described above the lip 133 formed at the junction of the input and middle housing restrains axial movement of the ring gear.
Gearboxes incorporating the above-described “floating” ring gear design and are not prior art, have been developed in which the input housing and middle housing are integrated as a single unit. However, if the middle housing portion of such an integrated unit has a lip at the junction of the input housing, the ring gear cannot be installed. Accordingly, a system or apparatus is necessary to restrain axial movement of a floating ring gear in a wind turbine gearbox that provides an effective installation of the ring gear.